Hybrid braking systems for motor vehicles normally include a hydraulic service braking system and an electrically operated service braking system, such as an electrohydraulic brake (EHB) or an electromechanical brake (EMB). The hydraulic service braking system is usually assigned to the front axle and the electrically operated service braking system is usually assigned to the rear axle of the vehicle.
When the brake pedal is operated, the braking force applied by the driver is boosted by a brake booster (vacuum brake booster) located in the hydraulic service braking system and a correspondingly increased braking pressure is applied to the brakes of the hydraulic system. The driver's braking wish is also measured by a sensor (braking value sensor) and the corresponding braking value is supplied to a controller, which activates the brakes of the electric service braking system under consideration of the predetermined braking-force distribution.
In certain driving situations, for instance when the vehicle is heavily loaded or when traveling up or down inclines, it may be helpful to adjust the braking-force distribution between the front and rear axles, to adapt the braking behavior optimally to the prevailing conditions. It is known to change the braking-force distribution by increasing or reducing the braking force in the electrically operated service braking system However, this affects the braking behavior of the vehicle, since this changes the total braking force. When the portion of the total braking force that is applied via the electrically operated service braking system is increased, for example from 30% to 50%, the total braking force also increases (during the same brake pedal operation). This means that the vehicle will respond differently to the application of the same pedal force or the brake pedal operation during the same pedal travel. This significantly impairs driving safety, since the driver must constantly adjust to changes in braking behavior.